Question

What is a positive deviation from Raoult's Law and its example?

Answer 1

1. Raoult's law states that the product of partial vapour pressure of the pure solvent and the mole fraction of the solvent equals the vapour pressure of the solution.
2. Mathematically, $$\begin{gathered} {\mathrm{P}}_{\mathrm{solution}}={\mathrm{X}}_{\mathrm{solvent}·}{\mathrm{P}}_{\mathrm{solvent}}^{°} \\ \mathrm{where} \\ {\mathrm{P}}_{\mathrm{solution}}=\mathrm{vapor}\mathrm{pressure}\mathrm{of}\mathrm{the}\mathrm{solution} \\ {\mathrm{X}}_{\mathrm{solvent}·}=\mathrm{mole}\mathrm{fraction}\mathrm{of}\mathrm{the}\mathrm{solvent} \\ {\mathrm{P}}_{\mathrm{solvent}}^{°}=\mathrm{vapor}\mathrm{pressure}\mathrm{of}\mathrm{the}\mathrm{pure}\mathrm{solvent} \end{gathered}$$
3. Positive deviation means in simple words that when the vapour pressure is supposed to be higher than the expected value.
4. Example- The mixture of Ethanol and Acetone shows a positive deviation.